1. Field of the Invention
The present invention relates to a range finder for a camera, which determines a distance to an object, and in particular to a camera range finder whose light-receiving means or light-emitting means is provided with electromagnetic shielding.
2. Related Background Art
Known as a camera range finder is the one employing a trigonometric ranging system. The range finder employing the trigonometric ranging system comprises a light-emitting unit constituted by an infrared LED, a projection lens, and the like for projecting light onto an object; and a light-receiving unit constituted by a PSD (position sensing device), a condenser lens, and the like. In such a range finder, the light-emitting unit projects light onto the object, and the light-receiving unit receives the light reflected by the object, whereby the distance to the object is measured on the basis of the imaging position of the reflected light in the light-receiving means. Consequently, in order to enhance the measuring accuracy in the range finder, it is important for the light-emitting means such as infrared LED and the light-receiving unit such as PSD to be disposed at accurate positions as designed. Therefore, in general, a mechanism is provided for adjusting the positions of light-emitting and light-receiving means.
Examples of such a camera range finder are specifically disclosed in Japanese Patent Application Laid-Open Nos. 1-287412 and 2-12010. In the range finder disclosed in Japanese Patent Application Laid-Open No. 1-287412, as shown in FIG. 1 thereof, a condenser lens is secured to the front portion of a bedplate, while a light-emitting element is attached to the rear portion of the bedplate so as to be horizontally movable and is urged forward and sideward respectively by two leaf springs, thus constituting a light-emitting unit. In the light-emitting unit in this range finder, two adjustment pins respectively placed horizontally and vertically can move the light-emitting element horizontally and vertically so as to minutely adjust the position of the light-emitting element with respect to the condenser lens.
In the range finder disclosed in Japanese Patent Application Laid-Open No. 2-12010, on the other hand, as shown in FIGS. 1 or 3 thereof, a light-receiving lens is movably attached to an AF unit frame, while a PSD case made of a metal is placed downstream the light-receiving lens. Accommodated within the PSD case is a PSD as a light-receiving element, whereby the PSD is shielded (electromagnetically shielded) by the PSD case.
The above-mentioned conventional camera range finders, however, yield the following disadvantages. Namely, in the former (disclosed in Japanese Patent Application Laid-Open No. 1-287412), since the light-emitting element is not shielded, light may not be projected stably onto the object. Also, in order to shield the light-emitting element, the light emitting element has to be shielded together with the leaf springs directly urging the light-emitting element, thus increasing the number of parts due to the shielding, and increasing the size of the mechanism for adjusting the position of the light-emitting element. In the latter (disclosed in Japanese Patent Application Laid-Open No. 2-12010), on the other hand, since the light-receiving lens whose position should be adjusted with respect to the PSD projects out of the AF unit frame, its adjusted position may shift in a subsequent step of making the range finder. Therefore, there is a strong demand for developing a technique for collectively overcoming the disadvantages in the former and latter range finders without using any complicated mechanism.